Today about 30 towers are preserved in the countryside of the island. They have been built by feudal Venetians in particular (and other Latin nobles) who used them as a base to exploit the real estate of the field they held. Their defensive line included battlements, murder holes, turrets, huge doors and small windows to protect the defenders. They were made of stone and had many floors and thick walls.

During the Venetian rule this was the strongest castle in Naxos. There used to be older fortifications, but what is seen today was built by the Venetians around the 13th-14th century to control the inland. They called it Apano Kastro to distinguish it from Kato Kastro, i.e. the castle of Chora. It had two lines of forts and its ruins include remains of houses, cisterns, temples etc. It stands on top of a hill between Potamia and Tragaia.

This is a very important castle, built on a steep hill in the fields of Sangri and Agiassos. According to researchers, it took its name after the abundant “apaliries”, a kind of bush that sprouts there. It was erected in the first years of the Byzantine era, though probably there was already a fortification in the antiquity, because part of the wall is prehistoric. It was abandoned in the 13th century with the arrival of the Venetians.